Switched digital communications networks such as e.g. ATM (Asynchronous Transfer Mode) networks are widely used for high-speed broadband data transport. In this type of network, once a call is established, it will use generally the same route for its life, unless a physical link of the route becomes unavailable, in which case the call is rerouted. Various routing criteria are used for centrally provisioning communication sessions between users of such networks. Some of the currently used criteria are cost of the route (that depends on the transmission medium), number of hops along a route (that depends on node processing capacity utilization), and bandwidth load of the respective route.
Since a communication network has at its disposal limited resources (link bandwidth and node processing capacity) to ensure efficient data transmission, efficient use of the resources is an important requirement. When traffic demand increases, a network may become congested, resulting in degraded network performance. On the other hand, for proper operation, a network must be implemented so as to avoid congestion. The simplest solution obviously is to increase the capacity of the network; however this solution is generally undesirable for evident reasons of costs. Other less obvious solutions in support of efficient network operation consist in applying preventive measures, of which the main one is load balancing. Load balancing attempts to fairly distributing the traffic over all the links of the network to avoid a local congestion in particular resources and to better utilize the resources across the network.
Currently, the most common criteria for load balancing are based on determining an aggregated BW (aggregated over multiple hops) for each possible route for a call, and selecting the route with the lowest aggregated utilization for a new call. This is for example described in the U.S. Pat. No. 6,697,333 (Bawa et al.) entitled “Bandwidth load consideration in network route selection”, issued on Feb. 24, 2004 to Alcatel. The patent describes load balancing methods applicable to both new calls and existing connected calls, using bandwidth load as a selection criterion in addition to route cost and number of link hops in a route. Particularly, the method described in the patent selects the path (route) for a call from alternative paths having equal least cost, and then equal least number of link hops, a path having the less average bandwidth represented as an aggregate of bandwidth usage for each link hop.
In order to successfully manage the traffic across a switched digital network, it is important not only to allocate sufficient bandwidth for each connection from the knowledge of the source characteristics and the network status, but also to take into account call priority. Call priorities specify the relative importance of calls in the network and ultimately the order in which calls can be restored or provisioned.
Keeping this in mind, the problem with this current approach is that the call priority is totally ignored during routing. With the solution provided by the above identified patent, calls that have a high priority might all be riding on a common link across the network; if this link fails for whatever reason, most of the high priority customer calls will fail at the same time and also be competing for resources during reroute time.
Thus, there remains a need to provide a new route selection method that also takes into consideration call/connection priorities, by load balancing the calls in a communications network based on call priority.